Commit 561a178

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Update Stack.md

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Original file line number	Diff line number	Diff line change
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	`1`	`+Evaluate Post fix expression`
	`2`	+```
	`3`	`+public int evalPostFixExp(String expr) {`
	`4`	`+ if(expr.equals(""))`
	`5`	`+ return 0;`
	`6`	`+ Stack<Integer> stack = new Stack<>();`
`1`	`7`
	`8`	`+ for (int i = 0; i < expr.length(); i++) {`
	`9`	`+ char c = expr.charAt(i);`
	`10`	`+ if (Character.isDigit(c))`
	`11`	`+ stack.push(c-'0');`
	`12`	`+ else if(isOp(c)) {`
	`13`	`+ int b = stack.pop();`
	`14`	`+ int a = stack.pop();`
	`15`	`+ stack.push(execOp(c,a,b));`
	`16`	`+ } else`
	`17`	`+ throw new IllegalArgumentException("Invalid input");`
	`18`	`+ }`
	`19`	`+ return stack.pop();`
	`20`	`+ }`
	`21`	`+`
	`22`	`+ private int execOp(char op, int a, int b) {`
	`23`	`+ switch (op) {`
	`24`	`+ case '+':`
	`25`	`+ return (a+b);`
	`26`	`+ case '-':`
	`27`	`+ return (a-b);`
	`28`	`+ case '*':`
	`29`	`+ return (a*b);`
	`30`	`+ case '/':`
	`31`	`+ return (a/b);`
	`32`	`+ case '^':`
	`33`	`+ return (int) Math.pow(a,b);`
	`34`	`+ }`
	`35`	`+ throw new IllegalArgumentException("Invalid Input");`
	`36`	`+ }`
	`37`	`+`
	`38`	`+ private boolean isOp (char c) {`
	`39`	`+ switch (c) {`
	`40`	`+ case '+':`
	`41`	`+ case '-':`
	`42`	`+ case '*':`
	`43`	`+ case '/':`
	`44`	`+ case '^':`
	`45`	`+ return true;`
	`46`	`+ }`
	`47`	`+ return false;`
	`48`	`+ }`
	`49`	+```

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